Measuring Nectar Secretion: The Example Of An F1 Hybrid And Its Male Sterile Parent In Winter Oilseed Rape (Brassica Napus L.)

During the evolutionary history of flowering plants, the appearance of floral nectaries allowed the replacement of pollen by nectar to attract pollinators, allowing lower costs involved in animal pollination by reducing the consumption of pollen. In the hybrid seed productions of entomophilous crops, knowing the levels of nectar secretion of the different lines, the male fertile (MF) and the male sterile (MS) ones, is important to maximize pollen transfers between them. In this study, we start with a review of current methods used to measure nectar secretion, and choose the one that provides a gross secretion rate in order to use it on two winter oilseed rape (Brassica napus L.) lines, the hybrid F1 'Exocet' and its MS parent. We show that oilseed rape has a gross nectar secretion rate that is constant over a period of 6-8 hours during daylight hours, that it has a thermal optimum included between 20 degrees C and 30 degrees C, and that the parental MS line secretes about half as much as the hybrid F1 one. These results enable us to propose a rigorous method to compare nectar secretions between lines and varieties. We conclude with the main other variables that should be taken into account to estimate the total amount of nectar produced by a given area of crop.